As a young boy involved in the heroic defence of Van, Arshile Gorky was witness to one of the most courageous moments in Armenian history, but the months and years that were to follow would see him lose a home, his people, and - most traumatically - his beloved mother."

I have often read these words from my book at public readings, but now I am no longer the author reading them. An actress has taken over in a movie called Ararat, directed by Atom Egoyan.

In November 1998, a few days before the launch of my biography, I received a handwritten fax from Ego Film Arts in Canada. "Dear Nouritza, I have tried to call you many times with no luck. I just wanted to tell you that Black Angel is a stunning piece of work, and that you should be very proud of this revelatory project. [In Armenian script] Sirov [with love], Atom."

He had caught me frantically preparing for my book launch, a solo performance of Gorky's life enacted through his four beloved women on stage at the Royal College of Art. There is a myth about "a Gorky curse" and this book, over many years, cost me a small fortune and sent me on an obstacle course that I wouldn't wish on my worst enemy.

Egoyan and I had met before. He was soft-spoken and engaging. He had quizzed me about my research into Gorky's life. For Armenians, as for the rest of the world, the Armenian-American "artiste maudit" was an unfathomable mystery. Why did an Armenian throw away his name, Manoug Adoian? Why did he commit suicide? The questions were always the same.

I explained that, as a teenager, I had fallen in love with Gorky when I first saw his exhibition at the Tate. My heart stopped when I saw the dark-eyed portraits and jewel-like abstractions. Then I discovered that this great abstract artist was Armenian, like myself, and that his family, like mine, had suffered in the Armenian genocide.

I was determined to find out how this affected these amazing paintings and, ultimately, his suicide in 1948. His life had everything I needed as a subject for biography. I could learn about a traumatic Armenian childhood, an adventurous escape, and an inventive art that made him a master of a modern movement, the New York school. Tall and handsome, with heavy-lidded, soulful eyes, he was volatile and enigmatic. There would be so many secrets to unlock and connect.

Disguised as an English schoolgirl at boarding school, I had escaped the weight of my grandparents' tragedies: children killed, families split up, homes and land lost. The whole of my ancestry resonated as I delved into our history to write my book.

In the opening scenes of the film, Ani, an Armenian historian, launches her biography of Arshile Gorky: "The Artist and His Mother is not just a simple reproduction of a photo. Gorky's homage to his mother was bound to take on a sacred quality. The fact that he survived the Armenian genocide explains its spiritual power. Gorky saved his mother from oblivion by snatching her from a pile of corpses to place her on a pedestal of life." Egoyan had cut to the heart of my book.

In the film, a director, played by Charles Aznavour, is enchanted by Ani's story of Gorky's childhood in the siege of Van and asks if he can use her book. In real life, Egoyan asked to meet me in Paris. When we met, I did not recognise my book - it was tasselled with yellow stickers, highlighted and marked on every page. Egoyan told me that some passages had made him cry. He had tried to turn it into a script, but historical movies were not his cup of tea.

He asked me to listen to his storyline. "A woman writes a book about Arshile Gorky." He punched the air: "If there is any resemblance between you and Ani, please tell me now!" A book is one thing, a film another. I argued that the Gorky story could stand on its own. His was a truly epic life that encapsulated all the features of the Armenian genocide artist.

Gorky had come to America, aged 16, determined to become an artist. To paint was to survive a shattered childhood and stay connected to his lost paradise. No one had interpreted his art correctly because his heritage had been utterly ignored. This was the film I wanted to see made. But Egoyan would not be swayed, and I could not stand in the way of a fellow Armenian whose work I admired. I read the scripts and commented.

At last the film went into production, and the emails started arriving. "It's been six months! Just to let you know that work on Ararat is going very well. We are almost finished the editing. I'm running on adrenaline."

Inevitably, a sabotage campaign was unleashed by Turkey, which gave the film huge publicity. It was released across the world to great success: in Moscow, audiences spilled outside the kinos; Yerevan, the capital of Armenia, was ecstatic; in the US Ararat came second only to Harry Potter, while it won several awards in Canada. I wondered about Britain, hot on Egoyan but lukewarm on the genocide. How was Egoyan feeling about it all now?

Last week came another email: "I can honestly state that your book was extremely liberating. It conjured such a vivid portrait of Gorky that I felt I could interpret and take presumptions that I would never have given myself permission to take otherwise. In a sense, your book was something shockingly authentic and emotionally exposed."

Everyone knows that often, when authors see their books on screen, they wish they had never written them. But I was blown away at the Cannes film festival when I first saw the dark-eyed figure I had imagined as Gorky in my book, and even myself, as an Egoyan character, on the screen. By the end of the screening, I knew that the 83-year taboo of repressed Armenian history was over. My grandparents became homeless, childless, disinherited. Egoyan's too. "When I see these places," says one character, Raffi, standing before a threatened 10th-century church, "I realise how much we've lost. Not just the loss of land and the lives, but the loss of any way to remember it."

Egoyan had blown open the taboo genocide of the 20th century. The fact that he had succeeded in filming and screening it was enough. But it is also an ambitious, psychological investigation and a landmark in film-making. As for me, I am glad to have played a part in it.

· Ararat is released next Friday. Nouritza Matossian's Black Angel: A Life of Arshile Gorky is published by Pimlico Press. A preview introduced by Matossian is at the Curzon Mayfair, London W1 (020-7495 0500), on Wednesday.